A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen to guide the user to a destination.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system for route guidance to a destination. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen.
An example of process for specifying a destination in the navigation system through a Point of Interest (POI) search method is shown in FIGS. 1B-1F. FIG. 1B show a “Find Destination by” screen for specifying an input method for selecting the destination. The “Find Destination By” screen lists various methods for selecting the destination including “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest (POI)” for selecting the programmed destination based on the name, category or telephone number.
When selecting, the “Point of Interest” method in FIG. 1B, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1C. The “Place Name” is to specify a name of the intended POI, and the “Place Type” is to specify a category of the intended POI. If the “Place Name” is selected in FIG. 1C, the navigation system displays a keyboard screen so that the user inputs the desired POI name as shown in FIG. 1D.
In FIG. 1E, as the user enters characters of a place name or specifies a particular place type, the navigation system will narrow down the candidate place name by searching a map database. FIG. 1F shows a screen where the candidate POI name is displayed thereon as a result of the user's input. In FIG. 1G, when the user confirms that the candidate POI is a desired place to go, the navigation calculates an appropriate route to the destination. After determining the calculated route to the destination, the navigation system starts the route guidance operation as shown in FIG. 1H.
The majority of map data in the map database for the operation of the navigation system accounts for data directed to roads and links which are configured by large number of road segments. Each road segment is a small unit of line typically defined by at least two absolute locations, i.e., a start point and an end point. The map database also includes a large amount of data concerning points of interest (POIs) which express place names, addresses, phone numbers, etc. of restaurants, gas stations, shops, banks, ATMs, companies, hospitals, etc. Such POI data is arranged in a POI database within the map database.
The map database also includes polygon data which defines a two dimensional shape of an object. Typically, the polygon data define bounded regions of relatively large structures such as high rise buildings, factories, airports, stadiums, shopping malls, schools, etc., and natural objects such as lakes, rivers, mountains, fields, etc. The amount of polygon data has been increasing in the recent map database for achieving an improved performance of the navigation system.
In many occasions, such polygon objects defined by the polygon data are also points of interest (POI) and thus the information thereon may be stored in the map database as POI data. Consequently, shopping malls, buildings, schools, airports, etc., defined by the polygon data can be searched through the POI search method as described above without using the polygon data. The route guidance operation to the selected polygon object (POI) can be done by the well established functions of the navigation system. However, currently, there are polygon objects that are defined by polygon data that are not associated with any POIs, i.e., not included in the POI database.
As noted in the foregoing description for finding a destination for the route guidance, the POI search method is often used because this search method is well established in the industry with use of place name, place type, phone number, etc. When the user has a particular destination in mind that involves polygon data but is not associated with a POI, such as a name of a particular building, finding the location poses a problem. Further, when the user recognizes the name of a building but does not know any POIs associated with the building, it is difficult to find the building since the POI search method will not produce the name and address of the building.
Therefore, there is a need of a new search method and apparatus for searching an object that is defined by polygon data but is not associated with any POI.